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and Webb, 1990) Sediments in the vicinity of the site generally consist of reddish- brown to dark gray clayey silt with moderate to well sorted, fine sand lenses The Central Valley is drained by two large river systems- the Sacramento River (northern part of the Valley) and the San Joaquin River (most of the southern part of the Valley). The two rivers meet about 13.6 miles northwest of the facility The closest surface water features are the easternmost reach of the Port of Stockton, approximately 1,000 feet north-northwest of the facility, and Mormon Slough, located approximately 1,300 feet southwest of the facility (Figure 1) Historically, groundwater in the Stockton area has typically occurred under water /?f( table conditions at a depth between25 and 35 feet (Infurna, 1991). Severe drought conditions during recent years combined with the intense agricultural development have lowered the water table to below 40 feet. ' Groundwater flow direction in the area is influenced primarily by the Port of Stockton Channel Influence by the smaller Mormon Slough is expected to be seasonal, moving laterally away from the Slough during high precipitation periods. ' Based on water level measurements taken on August 30, 1994, the present depth to water at the facility is approximately 41 feet. Groundwater flow is to the south with a hydraulic gradient of 0.003 feet Mr foot. ' Local Surface Water and Groundwater Use The City of Stockton obtains its municipal and industrial water supplies from a combination of treated surface water and numerous groundwater supply wells located in and around Stockton. According to the State of California, Department of Water Resources well records, no domestic or mtable water supply wells are located within 1 mile of the Greyhound facility ' SITE NVESTIGATION Soil Boring and Soil Sampling Procedures ' In August 1994, a total of eight additional soil borings (SB-1 through SB-8) were advanced at the locations shown on Figure 2 to characterize the lateral and vertical ' extent of hydrocarbon contamination at the site. Each of the borings was advanced to depths between 45 and 51.5 feet using 4 25-inch inside-diameter hollow-stem augers and split-spoon sampling techniques in accordance with ASTM-Standard D-1586. Prior to advancing each boring, all downhole equipment was decontaminated by steam- cleaning. All drill cuttings were containerized in labeled DOT-approved, 55-gallon drums, and left on-site for proper disposal by Greyhound at a later date. Soil samples were collected for laboratory analysis in 6-inch long brass sample tubes that were inserted into a 1.5-foot-long split-spoon sampler at 5-foot intervals. Soil sampling protocol consisted of capping each end of the brass tube with teflon tape and non-reactive, plastic end-caps The caps were then sealed with clear tape. A chain-of-custody record accompanied each soil sample container from selection and preparation at the laboratory, during sample collection at the site, and through analysis at the laboratory Each sample was individually labeled, identified in the field notebook, immediately packed in ice, sealed inside an insulated shipping container, and PAMSYROBVOLI WAM386 08969125386R02 DOC